Founder of 350.org, an environmental campaign aimed at holding atmospheric carbon dioxide concentrations below 350 parts-per-million, McKibben set this Saturday as the day to take to the streets.

The call went viral in ways far beyond anything McKibben and fellow organizers imagined: As of Thursday morning some 4,227 actions and rallies are planned in 170 countries, with 300 events in China, 1500 across the United States, 500-plus in Central and South America.